Welding apparatus and method of welding



Dec. 7, 1943. ADAMS, JR 2,335,894

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet l A mm,mi

Dec. 7, 1943. J. L. ADAMS, JR 2,335,894

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet 2 l I flVENTOR Dec. 7, 1943. .J. L. ADAMS, JR

WELDING APPARATUS AND METHOD OF WELDING IIIIIIIIIIII/ IIQLEYNTOR l3 Sheets-Sheet 5 Filed May 20, 1930 Dec. 7, 1943.

J. ADAMS, JR 2,335,894

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet 4 4 f; \H\ 'z i' l g 25 l Dec. 7, 1943. J L. ADAMS, JR 2,335,894

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet 5 Dec. 7, 1943. J. L. ADAMS, JR

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet 6 INVENTOR I I L l l I Dec. 7, 1943. J. L. ADAMS, JR I 2,335,894

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet 7 Dec. 7, 1943.

.J. ADAMS, JR 2,335,894

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet 8 Dec. 7, 1943.

J. L. ADAMS, JR

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet 9 lllEi-g iii . I 1 I I 1.:

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J. L. ADAMS, JR

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet l0 INVENTOR X M ZAQ %m,mxm

Dec. 7, 1943. D JR 2,335,894

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 13 Sheets-Sheet ll INVENTOR mx/iwg Dec. 7, 1943. .1. 1.. ADAMS, JR

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 15 Sheets-Sheet l2 74m; VMW/ I a Dec. 7, 1943. .1. L. ADAMS, JR 2,335,394

WELDING APPARATUS AND METHOD OF WELDING Filed May 20, 1930 15 Sheets-Sheet l3 INVENTOR A Maw, XWZDQWX @W, m, W/M

Patented Dec. 7, 1943 WELDING APPARATUS AND METHOD OF WELDING James L. Adams, Jr., Youngstown, Ohio, assignor to The Youngstown Sheet & Tube Company, Youngstown, Ohio, a corporation 0.1, Ohio Application May 20, 193%, Serial No. 453,838

(El. era-s) 24 Claims.

The present invention relates broadly to the art of electric welding, and more particularly to an improved method and apparatus for either the continuous or intermittent welding of metablic shapes and articles, and especially the welding of tubular shapes.

This is in part a continuation of my co-pendlug application, Serial No. 297,962, filed August '7, 1928, for Method and apparatus for welding (now Patent No. 2,181,445, dated November 28, 1939).

Ihe art of electric Welding has undergone a rapid development during the last few years. Up to the present time, however, while welding processes and machines have been produced and operated for the continuous or intermittent welding of materials, such as tubular shapes, they have been open to certain objections.

In the first place, most commercial installations have been designed to operate on the basis of supplying current by means of stationary or moving contacts in engagement with different portions of the pipe surfaces. In order to secure efficient operation or such types of apparatus, it has been necessary in most cases to subject the material to a preliminary cleaning, such as an acid dipping, or a mechanical surfacing operation either at the seam or adjacent the edges, or both, in order to insure not only a clean seam, but also the proper contact conditions for the input of the necessary welding current.

The present invention provides a method of welding which is not dependent upon any precleaning or special treatment of the sheets or other materials which are to be welded. This constitutes a distinct advantage in the art in that it eliminates an expensive handling and pretreatment operation. When it is considered that the mere mechanical handling of material of the character herein contemplated, not including any treatment, represents an expense in the neighborhood of 25 cents per ton, it will be appreciated that advantages result in direct proportion as the number of handling operations is reduced. Acid dipping, sand blasting, or mechanical surfacing near the edges, will add about 75 to $1.25 per ton more.

Commercial welding operations have further been characterized by distinctive types of welds, among which may be mentioned the stitch type and the surface type. While welds of these types are commercially successful for certain purposes, materials characterized by such welds cannot be used for all purposes in view either of the comparative mechanical weakness of the welds or the 6 nonmniformity thereof. it is on of the purposes of the present invention to provide a weldthe method which shall be characterized by the the production of a continuous weld throughout the complete thickness of the material and of uniform characteristics throughout the length of the seam.

Difliculty has also been encountered in commercial installations in the handling of materials having a considerable thickness. While commercial methods are adaptable to the Welding of materials up to a thickness or" perhaps one-fourth of an inch, they have not been commercially suitable to materials having substantially greater thicknesses. it is a further purpose of the present invention to provide a welding method and apparatus which may be effectively utilized with materials of the maximum thickness ordinarily encountered in commercial articles such as it is desired to produce by a Welding operation.

The present method and apparatus, for example, will effectively weld material having a thick ness of one inch at a rate in the neighborhood of 30 to feet per minute. This is given by way of euample only and not by way of limitation inasmuch as the construction of the machine and the variable current input enable different welding speeds with different thicknesses of material to be satisfactorily obtained, within certain limits.

Heretofore in the art of welding there has been a further commercial difficulty having to do with the production of substantially straight tubular articles, 1. e., articles free of camber. With known methods of welding, at least insofar as I am familiar with them, it has been impossible to produce an article sufiiciently straight so as not to require a subsequent straightening operation to remove camber therefrom. This has, I believe, been due to two major factors. One of these has been the relatively great area of the complete article which has been subjected to an appreciable heating operation, and the other has been the relatively slow speed at which heating from end-to-end has been accomplished.

In accordance with the present invention I am able to effect a weld under such conditions that the heating is concentrated almost entirely at the seam, so that the major expansion tendency lies in too small a per cent of the total metal present to pull the latter out of its initial alinement very materially, and at such a speed that with a given piece of material the weld is effected with such rapidity that substantially uniform temperature conditions at the scam, in-

sofar as their effect on the shape of the article 1 is concerned, can be obtained.

From a commercial standpoint, therefore, the present method and apparatus may be briefly characterized by the following attributes:

1. The entire absence of pre-cleaning or pretreatment of material.

2. Continuity or uniformity of weld throughout the thickness and length of the seam.

3. Effective welding of materials irrespective of the thickness thereof, within Wide limits.

4. Maintaining'the articles substantially free from camber or other deformation by reason of the welding temperatures.

Advantageous results of the character referred to are obtained by an inductive method of current input, as distinguished broadly from a contact method of current supply.

with the contact method of welding in which a mechanical or electrical contact is necessarily established between the material to be welded and a suitable conductor, there is a very appreciable as well as a variable loss in the current supply during the operation of continuous welding. This is true regardless of whether the contacts move with the material or not, inasmuch as diflerent contacts are in engagement with surface portions of different conducting characteristics. and inasmuch as the individual contacts themselves, where movable with the material, are more or less spaced one with respect to the other. I

These conditions therefore necessarily result in different temperature conditions at different times and points, with a resulting irregularity or non-uniformity in the character of the weld. In addition to objectionable results of the character referred to, any contact method of welding, reg'ardless of the characteristics of the contacts, possesses the further disadvantage that due to the normally greater resistance in that path between the contacts, which includes the seam, as compared with the back path through the pipe, a very large portion of the energy supplied is wasted by heating the back portion of the pipe.

In actual practice this quantity varies in accordance with the inverse diameter of the pipe being welded, so that the total energy losses in the back path, and between the pipe and the contacts taken together, usually represents a very substantial, if not actually the greater portion, of the total energy input.

These disadvantages are in addition to the fact that with a commercial apparatus of the character which it has heretofore been possible to develop, and dependent upon the use of a current supply by means of a contact or contacts, it has not been possible to continuously weld pipes having a wall thickness much if any greater than to M; of an inch.

By supplying the heating current inductively, as before referred to, the objections and difliculties heretofore encountered with respect to contact types of welders either for resistance or flash welding, are obviated.

The present invention. although not limited to the so-called flash method of welding, is particularly adapted thereto, although it may be characterized by a combination of flash and resistance welding at different points progressively throughout the length of the material during the continuous movement thereof, as will be hereinafter more fully pointed out.

The flash method of welding, which is characterized by a relatively short flame condition spread substantially uniformly throughout a considerable portion of the length of an article, is the best possible method of quickly obtaining a uniform condition of the edges. An arc, as such, tends to concentrate itself at a relatively restricted point or points and produces an objectionable burning away at such point or points. A flash, on the contrary, will tend to removeany surface irregularities by a rapid planing off action and produce a substantially uniform edge condition.

This makes it possible to employ the flash method of welding without any accurate pretreatment or pre-cleaning of the edges of the material. 0n the other hand, if such material having uneven edges were subjected to a straight resistance welding, there would obviously be nonuniform resistance at different points throughout the length, thereby generally precluding the production of a uniform joint. A flash weld will take about one-half the k. w. input of the straight resistance type of weld, furthermore, or give double speed for the same input.

A flash method of welding is also characterized by the fact that it effects heating of high carbon spots. It therefore permits welding of non-uniform plate widths, as well as the welding of material having a non-uniform carbon content.

In the contact method of flash welding as heretofore carried out, it has been necessary for tremendous currents at low voltage to be fed into the work on one side of the seam and taken off on the oppo ite side through extremely heavy contact means applied under relatively great pressure to the metal surface.

It will further be apparent that any contact method of welding, regardless of the construction or arrangement of the contacts, and regardless of whether liquid or solid material is utilized, is necessarily characterized by a heavy current flow into the contact, and a second current flow out of the contact and into the material, as well as a tremendous abstraction of heat by its flow into these heavy water-cooled contacts from metal close to the seam. All of these difiiculties have therefore necessarily limited the contact method to relatively low current values and consequently have limited the gauge of the material which could be successfully welded thereby.

- With an induction welding apparatus, on the contrary, the only limit to the amount of current which can be supplied to the material for welding purposes is that determined by the capacity of the apparatus itself.

In the accompanying drawings I have shown for purposes of illustration only, certain preferred embodiments of the present invention.

In the drawings,

Figure 1 is a view, partly in side elevation and partly in section, illustrating one form of apparatus constructed in accordance with the present invention,

Figure 2 is a top plan view of the apparatus illustrated in Figure 1,

Figure 3 is an end elevational view of the apparatus illustrated in Figures 1 and 2, certain of the parts being omitted for sake of clearness,

Figure 4 is a transverse sectional view on the line IV--IV of Figure l certain of the parts being shown in elevation,

Figure 5 is a detail sectional view illustrating a preferred form of construction of the working rolls utilized,

Figure a is a view similar to Figure 5, illustrating the parts in locked position,

Figure 6 is a side elevational view 01 the preferred form of carrier frame,

Figure 7 is a detail view, on an enlarged scale, of a modified embodiment of my invention for obtaining confining of the almost molten material at the actual point of closing the seam,

Figure 8 is a side elevational view of another form of apparatus constructed in accordance with the present invention,

Figure 9 is a vertical transverse sectional view on the line IX-IX of Figure 8, looking in the direction of the arrows,

Figure 10 is a transverse sectional view on the line x-x of Figure 8, looking in the direction of the arrows,

Figure 11 is a transverse sectional view on the line XIXI of Figure 8, looking in the direction of the arrows,

Figure 12 is a detail sectional view, on the line XII-XII of Figure 8, looking in the direction of the arrows,

Figure 13 is a top plan view of a portion of the apparatus illustrated in Figure 8,

Figure 14 is a horizontal sectional view along the line XIV-XIV of Figure 8, looking in the direction of the arrows,

Figure 15 is a vertical transverse sectional view, on an enlarged scale, along the line XV-XV of Figure 8,

Figure 16 is a partial longitudinal sectional view, on an enlarged scale, through the pipe being welded,

Figure 17 is a detail sectional view along the line X JII-XVII of Figure 16,

Figure 18 is an enlarged sectional view or" one of the coils,

Figure 19 is a perspective view, partly broken away, and illustrating a slightly modified embodiment of the invention,

Figure 20 is a diagrammatic view illustrating the repelling or repulsion effect produced by the utilization of an inner coil,

Figure 21 is a detail view of a modified form of inner coil construction,

Figure 22 illustrates a further modification of an inner coil in which the number of sections is increased,

Figure 23 is a transverse sectional view, on an enlarged scale, through the inner core and coil assembly along the line XXIII-XXIII of Figure 1,

Figure 23a. is a top plan view of a portion of one of the protective sections for the inner core and coil assembly,

Figure 24 is a plan view of the under side of one of the protective sections for the inner core and coil assembly.

Figure 25 is a detail view of one form of mechanism for smoothin the joint,

Figure 26 is a top plan view of one form of feeding mechanism,

Figure 27 is a detail sectional view on the line XXVIIXXVII of Figure 26,

Figure 28 is a view similar to Figure 25 illustrating still another embodiment of the invention,

Figure 29 is a sectional elevational view of a slightly modified form of a rearward extension of the inner coil and core assembly,

Figure 30 is a transverse sectional view on the line XXX-XXX of Figure 29,

Figure 31 is a top plan view of a portion of the roller guide strip of Figures 29 and 30, and

Figure 32 is a detail sectional view of one of the roll housings of Figure 29.

While inductive welding in accordance with the general p ple of the present invention may be accomplished by the utilization of both inside and/or outside cores and/or coils, the characteristic results obtained by the different types of machine are fundamentally different. Under the temperature conditions to which the material must be subjected when it is being raised to a welding heat, there is of course a tendency for the molten and/or gaseous material to flow.

I have found that such flow may be very effectively controlled electrically in such manner as to produce at least a predominating flow of molten metal, vapors and impurities outwardly, so that the seam is effectively cleaned 0f any foreign matter, the impurities delivered to the outside of the article, and a clean joint insured. This can be obtained in. accordance with the present invention by the utilization of an inside coil constituting a current carrying conductor, and by utilizing the material being welded as a moving secondary for such coil in such manner that when the seam metal is heated to molten condition and vaporized under the temperatures created, there will be a magnetic repulsion between the inner coil as one conductor and the seam metal vapor as the other conductor. From a commercial standpoint this constitute a distinct advantage over welders as heretofore constructed and used.

These various features will now be taken up in detail so that a clearer and more complete understanding or" the present invention may be had. For this purpose Figures 1 to '7, 21, 23 and 2d of the drawings will first be considered.

In the preferred embodiment of my invention the welding is accomplished entirely within or between two roll passes. In order to provide these roll passes, I utilize two main frames 2: and each of which will hereinafter be referred as housings. The two housings are of generally similar construction, the details or one of the housings being illustrated in Figure 4. From this figure it will be apparent that the housing, which is preferably of steel and of special construction to withstand the tremendous strains to which it is subjected, is so shaped as to provide a series of roll-receiving openings 4, the openings facing the axis of the housing. Intermediate these openings are shaft bearings 5 or" any preferred construction adapted to coopcrate with the ends of the shafts 6 which are journaled therein.

Surrounding each of the shafts is an eccentric sleeve 7, all of which sleeves are of generallysimilar construction. All of these sleeves, with the exception of the two sleeves cooperating with the shafts 6 located in the upper portion of the housing on opposite sides of the center line thereof, are formed with bevelled gears 8 on one end preferably integral with the sleeve, and with bevelled gears 9 on the opposite end, preferably formed on removable collars screw-threaded into position on the sleeves and held against accidental removable by suitable keys I0. These gears, as will be apparent from Figure 4, are intermeshed with each other in such manner that rotation of one of the sleeves insures a corresponding rotation of all of the sleeves.

Such a rotation may be obtained by providing in each of the housings a shaft ll carrying at its inner end a bevel pinion i2 meshing with one of the gears on one of the sleeves], and carrying at its outer end a worm wheel l3.- Cooperating with this worm wheel is a worm Hi adapted to be rotated in any desired manner as, for example, by a hand wheel I5.

This hand wheel may be provided with teeth or ratchets l6 adapted to be engaged by a stationary pawl, rack or other holding means I? whereby the parts may be held against accidental movement from any predetermined adjusted position. From the construction described, it will be apparent that rotation of the hand wheel 15 effects a corresponding simultaneous rotation of all of the sleeves l in one direction or the other.

Carried by each of these sleeves is a work roll it, all of which are of generally similar construction, and all of which, with the exception of the two in the upper portion of each of the housings on opposite sides of the center line, are provided respectively with teeth l9 and 20, whereby all of the rolls may be directly intergeared in a manner similar to the intergearing between the respective sleeves.

Due to this construction, rotation of one of the working rolls effects corresponding and concomitant rotation of all of the rolls. This rotation may be accomplished by providing a drive shaft 2| in each of the housings, preferably opposite the adjusting shaft II, and mounted in suitable bearings. Each drive shaft carries at its inner end a driving pinion 22 meshing with the teeth on one of the work rolls. At its outer end the drive shaft may be provided with a worm wheel 23 adapted to be driven by a driving worm 24 from any suitable source of power, such as an electric motor, not shown. It will be understood that the driving worms 24 for the separate housings may be driven either by a common shaft or by separate shafts as desired. In most cases, however, the working rolls will be driven at approximately equal speeds so that separate drives are not necessary.

The construction of the various gears I9. 20 and 22 is such as to provide for some relative radial movement therebetween, this relative movement being suihcient to enable all of the work rolls to be simultaneously adjusted toward or from the axis of the housing by means of the rotation of the eccentric sleeves l as before described. There is thus provided a mill including in each of its housings five working rolls adapted to be simultaneously rotated in the same direction, and capable of simultaneous adjustment toward or from the axis of the housing so as to accommodate them to articles of different diameters and to enable the degree of pressure applied to the material, as well as the final diameter of the article, to be varied at will.

The sleeves 1 and working rolls l8, lying in the upper portion of each of the housings and on opposite sides of the center line, differ in construction from the other corresponding parts -only in that their adjacent ends are adapted to be spaced from each other, as clearly indicated in Figure 4, and not intergeared. This provides a space S, which in actual operation of the apparatus breaks the continuity of the metal conducting path which would be established if all of the sleeves and rolls were intergeared at this point. This break in the path is particularly important, as will be hereinafter more fully pointed out.

While I have described in detail only one of the housings, it will be apparent that the housings may be of generally similar construction and adapted for similar operation. The description of one will therefore sufiice for both.

Intermediate the housings 2 and 3 is a roll carrying frame 25, shown in detail in Figure 6, for a plurality of combined pressure and holding rolls 25, any desired number of which may be provided. The carrier frame is of such construction that the pass provided by the rolls 26 may be enlarged or diminished by contracting or expanding the frame. This adjustment may be effected by utilizing a split or yieldable frame 25, as clearly shown in Figure 6, and providing a shaft 2? having oppositely threaded portions in engagement with the respective sections of the carrier. By reason of this construction, rotation of the shaft 21 in one direction will be effective for bringing the rolls 26 closer together, While rotation in the opposite direction will be effective for expanding the same.

While a split or yieldable frame of the character just referred to is effective for producing minor adjustments of the holding rolls 25, provision must be made for effecting major adjustments thereof in case of any substantial change in the diameter of the articles bein welded. The construction illustrated in Figure 6 enables this to be accomplished by the bodily removal of the holding rolls 26 and the brackets 26' in which they are mounted, and the insertion of suitable shims or other spacing means intermediate the bases of the brackets and the pads 25' provided therefor on the carrier frame. By inserting shims or spacing means of uniform thickness behind each of the brackets, the desired relationship of all of the holding rolls can be maintained.

Positioned in the upper portion of the housings 2 and 3 and extending continuously therethl'ough in a plane intermediate the upper Work rolls l8 of the respective housings, is a laminated yoke 28. Cooperating with this yoke is a pole piece 29, which is also preferably laminated, and which is provided with a central opening of somewhat greater diameter than the maximum diameter of the material to be welded in the apparatus. Cooperating with the central opening in the pole piece 29 are individual pole pieces 30, each projecting forwardly toward the actual center of the pass of the working rolls in the housing 2, as will be clearly apparent from Figure 1 of the drawings. I have found that very advantageous results are obtained by so constructing the individual pole pieces that they are effective for providing a magnetic flux path extending well within the zone defined by the outer peripheries of the working rolls IS in the housing 2.

The desirability of such a construction and arrangement of the parts will be hereinafter pointed out. From Figure 3 of the drawings, however, it will be apparent that these individual pole pieces 30 constitute an approximately continuously extending magnetic path closely cooperating with the exterior of the material M illustrated as being operated upon by th apparatus.

Where it is desired to utilize the apparatus for relatively short lengths of material, I preferably provide a second pole piece 3|, similar to the pole piece 29, but on the entering side of the housing 3. Experience has shown that improved results are obtained if the pole piece 3| is placed on the exit side of the housing 3, as shown in Figure 28, since it is then unnecessary to continuously initiate the flash by momentary contact at that point between progressing edges. This pole piece is similarly provided with a central opening of greater diameter than the maximum diameter of the material to be worked upon, and carries an inner laminated liner 32 adapted to directly receive th material M, but without contact therewith.

In view of the well known fact that magnetic flux in entering laminations through the broad side will produce an objectionable heating up of the same, I preferably provide in the yoke 28, and in line with each of the pole pieces 29 and 3| a series of plug inserts 33 characterized by laminations so disposed and arranged that magnetic flux may pass continuously through the magnetic circuit provided, while travelling at all times into and out of any given lamination in an edgewise direction.

Where the apparatus is designed for use with relatively long pieces of material or for continuous welding-up operations, the pole piece 3i and its cooperating parts may be dispensed with entirely. In such cases the magnetic yoke 28 may be continued rearwardly in the form of an overhung laminated beam 34 suitably supported by struts or stay 35 from the housing 34, the beam 34 being of suitable construction to provide the desired continuation of the flux path established by the yoke 28, such laminated continuation extending clear down to a central core 38 and being integrally associated therewith. In such case, however, it is better not to try to crush th tube, or even to contact its edges in this stand, since too great profusion of spittings is thrown off thus necessitating repeated cleaning of the rolls, without compensating advantages.

From the foregoing, it will be apparent that I have utilized the terms continuous welding and intermittent welding not as defining different characteristic operations, but as defining operations with respect to the material worked upon. The term intermittent as utilized herein has reference to individual lengths of material,

while the term continuous has reference to operations characterized by the welding-up of lengths of material greater than those which have ordinarily been considered as representing commercial pipe lengths.

Where, however, the pole piece 3| is to be utilized, the beam 34 will be constructed entirely from the standpoint of the mechanical load which it is designed to carry and not from the standpoint of providing a flux path. In such case, the splice plates 31 may be of non-magnetic material, so that a closed magnetic path is not provided between the beam and the inner assembly 36, shown in detail in Figure 23. In such case, furthermore, the inner assembly will include an inner pole piece 39 approximately in the plane of the ends of the individual pole pieces 30. With such a construction, the magnetic path will be provided, for example, from the pole piece 39, to the individual pole pieces 30, to the pole piece 29, thence to the yoke 28, and by way of pole pieces 3| and liners 32 into the inner pole piece 38 and thence on through the core of the coil. This path, as will be apparent particularly from Figure 1 of the drawings, will include two air gaps each of suflicient dimensions to receive the material being welded.

Where, however, a continuous welding operation is practiced which is not dependent upon the employment of the pole pieces 3|, 32 and 38, they may if desired be completely eliminated and a magnetic path directly established at the entering end of the apparatus between the beam 34 and the inner assembly by a construction of the character hereinbefore referred to. This improves the working conditions inasmuch as it provides a magnetic flux path having only a single air gap represented by that necessarily provided between the outer individual pole pieces 3|! and the inner pole piece 39.

Cooperating with and carried by the inner assembly is a coil 40 having leads 4| and 42 extending rearwardly through the assembly and connected to a suitable source of electric current not shown. This current, will, however, prefer ably, be derived from a moderate voltage source of suflficient power capacity for an inductive welding operation of the character herein contemplated.

With the construction thus described, a Piece of material M bent to substantially tubular form may be fed into the apparatus over the inner assembly, and beneath the beam 34, and into the path of the working rolls in the housing 3. These working rolls will be effective in some cases for crushing the tube to uniform size, or again for bringing the opposed edges of the material into the desired adjacent or abutting relationship, while preferably retaining the same out of contact one with the other. Thereafter the material will travel into the pass provided by the adjusting rollers 26, which may be so adjusted as to maintain proper spacing between said edges. During this time the material will have traveled over a portion of the coil 40.

Continued travel of the material will cause it to pass over the remainder of the coil 40 and also overthe inner pole piece 39 and into the plane of the axes of the working rolls in the housing 2. These rolls will be efiective for further deforming the material and for bringing the edges into actual contact under such pressure conditions that the desired weld may be efiected.

In actual practice the relationship of the parts may be such, for example, that the edges will come into contact at some point intermediate the rolls 26 and the plane of the axes of the Working rolls in the housing 2. As the edges are first brought together, it being assumed that the coil 40 is energized, a short circuit condition results in the material M, which material constitutes a moving secondary. This results in the production of a very short are or flash, which tends to travel or spread backwardly a very appreciable distance along the seam. This flash condition having been initially created, is thereafter substantially uniformly maintained in space irrespective of, and during, the travel of the material forwardly through the apparatus.

From the actual point of contact rearwardly to the point at which the flash does not occur, there is provided a zone which may be designated as the flash zone, while from the point of first contact to the plane including the axes of working rolls in the housing 2, there exists what may be designated the resistance heating zone, in which the edges, heated to a welding temperature, are in intimate contact. By properly adjusting the rolls 2B, the extent of the flashing zone may be varied as well as the actual division between the flashing and resistance zones. The separation between the edges in the flash zone leads to a greater voltage across the seam, and consequently a much greater percentage of energy input to the seam itself than is the case for plain resistance welding.

The greater the extent of the gap, so long as the arc is not extinguished, the greater the voltage across the gap and the greater is the fraction which it represents to the total-generated in the single turn of the movable secondary. This being true, the gap takes a correspondingly greater fraction of the total energy put into the single turn of the secondary, and the PR. losses through the back path provided by the metal represent a correspondingly minor fraction of the total energy input so long as the pipe diameter involved is not over two or three feet.

This being true, it will be apparent to those skilled in the art that. substantially all of the current going through the pipe represents actual welding current, the potential drop across the gap acting as a controlling factor for the total current flow. This is distinctly different from the old so-called contact type of resistance welding in which the current flow through the back path is not directly limited by the voltage across the seam, and in which the current in the back path may rise to tremendous values, all of which values represent total losses.

portion of the secondary and would therefore be subject to objectionable heating up. Such heating would not only be objectionable from the standpoint of the installation itself, but also from the standpoint of the tremendous losses which such heating would represent.

The provision of the coil on the inside of the material being welded is not only extremely desirable from the standpoint of the welding characteristics of the apparatus, but also from the standpoint of constructional characteristics. These welding characteristics will first be referred to, reference for this purpose being had to Figure of the drawings. In this figure the material M is shown as having its adjacent edges m and m in slightly spaced relationship, this figure representing a condition such as exists in the flash zone before referred to. In this zone the heating will be such as to bring the temperature of the material to a point at which a portion thereof will be vaporized. This vaporized metal will act as a secondary conductor spaced from the coil 40 which constitutes a primary conductor, and in which th current flows in the opposite direction from that induced in the vapor.

This being true, there is a magnetic repulsion between the two conductors. Since the conductor provided by the coil is not free to move, the vapor V will be forced outwardly in the manner indicated in Figure 20 to an extent determined by the repulsion, this in actual practice having been found to be great enough to effectively clear the heated joint of any foreign material, so that when the edges are subsequently brought into contact there is nothing to prevent the formation of a substantially perfect weld.

This outward repulsion of the vapor possesses the decided advantage of completely freeing the edges which are to be brought together to form the seam, of any impurities, whereby when the edges are finally brought into engagement with each other for closing the seam, only pure metal is included in the seam itself. This obviously aids very materially in the production of a weld which is not only more nearly perfect, but which is more nearly uniform from one end to the other.

This represents a further advantage of providing a flash zone preliminarily to the final closing up of the seam, inasmuch as an operation characterized by a continuous maintaining of the edges in abutting relationship would necessarily be such as to prevent the obtaining of any outward repulsion ffective for producing a scavenging or cleaning action. So far as I am aware, it has heretofore never been proposed to provide a coil inside of a pipe and utilize the characteristic action thereof for cleaning the joint and freeing it of impurities. It will be apparent that such a condition could not be obtained in an apparatus utilizing only an inner core, since a core constitutes merely a flux carrier, while a coil constitutes a dynamic factor or actual flux producing means.

The amount of the repulsion increases with extreme rapidity as the two conductors are brought toward each other and decreases as the conductors are moved apart. With any very appreciable distance interveningbetween the two conductors, there is provided an air and metal space of such dimensions as to accommodate a substantial fraction of the magnetic flux of the primary and/or secondary conductors, so that the energy transfer, as well as the repulsion effect is very considerably reduced. From this it will be apparent that close association of primary and secondary is essential for high energy delivery, and that two conditions are desirable in order to obtain efiective cleaning of the joint.

One of these is the formation and maintenance of an appreciable zone in which the edges of the material are sufliciently separated to permit the generation and repulsion of vapors, and the other, the maintenance of a sufliciently close relationship between the two conductors such that no very large area air path for the magnetic leakage flux exists.

A further distinct advantage is inherent in the maintenance of this flash zone and its vaporizing of a portion of the metal of adjacent edges of the material. It will be understood by those skilled in the art that the volume of gases generated when the metal is vaporized will be in the neighborhood of 1000 times as great as the original volume of the metal so vaporized. This volume of gases continuously repelled in the manner referred to and even overflowing to some extent out of the other side of the seam, will result in maintaining a non-oxidizing atmosphere such that the formation of oxides and their subsequent inclusion in the joint is prevented.

Furthermore, if the vapors travelling at high velocity were permitted to travel inwardly, they would, upon striking the inner coil and core assembly, b condensed and solidified thereon, thereby resulting in an objectionable building up on the assembly. By means of the present invention this action is almost entirely obviated, so that cleaning of the inner assembly is not often required.

From a constructional standpoint, it will be apparent that the inner coil utilizes a space which is serviceable for no other purpose. If the coil were placed exteriorly to the pipe, it would necessarily result in much greater separation of the roll housings and a corresponding increase in the size of the apparatus with its consequent operating and functional disadvantages and difllculties. Certain of these objections would result directly from the increase in the difiiculties of maintaining the edges in the desired relationship for accurately controlling the flash zones and resistance zones. The major portion of the magnetic leakage flux between the primary and secondary traverses the air or other intervening material and extends longitudinally of the coil axis. When an inside coil is used, therefore, there is practically no leakage of flux in the exterior rolls and the outside guide parts external to the secondary constituted by the tube blank. The losses and heating resulting from any currents in such exterior elements are thus reduced to a minimum by my construction.

I may, if desired, provide the inner assembly with inner rolls 44 and 45 mounted with their axes 46 and 41 slightly offset, as clearly shown in Figure 1, or provide other equivalent means, so that they may be adjusted for increasing or decreasing their over-all dimension. These rolls are preferably effective approximately in the plane of the axes of the working rolls l8 and are so disposed that the roll 44 directly underlies the seam and tends to produce a smooth inner wall on the material. In actual practice, I prefer to construct these rolls of non-magnetic material, such as non-magnetic steel, although commercially satisfactory results are obtainable with ordinary gray cast iron rolls.

While there is not an abrupt cessation of heating when material with a heated seam has passed out of the plane of the pole pieces 30 and 39, there is a decided falling off in this plane in the amount of heat generated in the pipe. Heat losses by conduction as well as by radiation being continuous, it is apparent that if the distance between the point of maximum metal temperature and the point of completion of the welding is too great, the temperature may fall to such a point that a successful weld cannot be produced. By extending the individual pole pieces 30 in the general manner indicated in the drawings, and more particularly in Figure 1, it is possible to get these two points so closely adjacent that the desired temperature conditions may be maintained during the actual final closing of the seam. This disposition of the parts, permitted by the use of an inside coil, therefore constitutes an important operating advantage of the present invention, although it represents a construction which is not imperative for welding purposes.

From a practical standpoint I have found that this disposition of the parts in a welding operation such as that hereinbefore described permits the production of a joint having very desirable characteristics. By properly correlating the time of pressure application and the amount of pressure application to the time of heating, where the heating has been substantially entirely confined to the edge portions of the material, it is possible to produce a seam characterized by highly desirable grain structure. The ordinary welding operation, due to the manner of heating the seam material, permits a considerable heat transfer by means of conduction throughout a substantial portion of the tube area. It is of course well known that heat produces grain growth. This being true, any portion of the material which is heated beyond the thermocritical temperature has a larger grain size than that portion which is heated only to approximately such temperature. The portion heated to approximately the critical temperature only has a refined grain structure which is more desirable than the structure of the parent body ofthe material.

Due to the extreme rapidity by which heating is accomplished in accordance with the present method, and the fact that the flash limits the heat to the extreme edges immediately prior to the actual pressure application, the pressure can be great enough to extrude substantially all of that portion of the metal which has been heated beyond a thermo-critical temperature, thereby bringing the transition zones of material, characterized by refined grain structure produced by heating to the thermo-critical temperature, together at the seam. A seam produced in accordance with the present invention, therefore, in which the seam is freed of impurities and in which the transition zones are brought together at the seam, possesses a grain structure superior even to the grain structure of the parent body, and therefore has a greater strength.

In addition to this correlation of time of pressure application and amount of pressure application to the time and manner of heating, I may subject the seam at the time it leaves the working rolls 3 to the action of a cooling medium. This may be accomplished by providing a water jet w preferably in the form of an arcuate shoe overlying the seam and provided with any desirable number of outlets. The quantity of water will be so regulated asto not cool the material at the seam to a temperature much if any below the thermo-critical temperature, whereby any grain growth will be immediately checked and an actual refining will take place.

It will be understood that by suitable analysis of the seams, it can be easily determined whether the amount of cooling medium should be increased or decreased.

The separation of the heating zone into a flash zone and a resistance zone is highly desirable not only for the reasons pointed out, and including the fact that the gap determines the percentage of energy input to the seam, but for the further reason that a materially greater and more concentrated heating effect is obtainable by the flash method for a given amount of energy input than is possible by the resistance method. For this reason the working rolls in the housing 3 are not usually so set as to bring the edges of the material into contact during passage of the same therethrough. If the edges are contacted or crushed by these rolls, they are allowed to separate very slightly for a considerable distance thereafter. If the edges remained in continuous contact from one roll pass to the other, the energy input would be nearly tripled, and yet the weld which would be produced would not usually be as satisfactory. In fact, no purely progressive resistance induction welding has ever been carried out, to applicant's knowledge, and many attempts in this direction have resulted in failures in spite of the much improved apparatus available in making such attempts as compared with prior art structures.

Having regard for the difierent conditions encountered in the different zones, I have found that extremely desirable results may be obtained by constructing the inner coil in the manner ilulstrated more particularly in Figure 21, in which the coil is shown as comprising two sections 48 and 49, the section 48 being of a length generally comparable to the length of the flash zone, and the section 48 being of a length generally comparable to the length of the resistance zone. While, by reason of the low voltages utilized, it is not difficult to effect the desired insulation between the difierent coil sections, I preferably wind 

